In U.S. Pat. Nos. 3,161,223, 3,481,174, 3,482,427, 3,559,444, 3,817,075 and 3,872,755, there are disclosed sheet bending brakes for bending metal or plastic sheets as are used in siding on homes and buildings.
In my U.S. application Ser. No. 141,427 filed Apr. 18, 1980 there is disclosed a sheet metal brake comprising a frame having a fixed jaw and a movable jaw and an anvil member adjustable secured to the movable jaw. The fixed jaw has a clamping surface movable between workpiece clamping and non-clamping positions relative to the clamping surface on the fixed jaw. A bending member is hingedly connected to the fixed jaw. The movable jaw is releasably locked in workpiece clamping position by a structure that includes an oval shaped spring member having opposed ends and opposed walls. The member is pivoted at one end to the movable jaw and at the other end to a handle for manipulating the jaw.
Among the objects of the present invention are to provide a sheet bending brake of the aforementioned type wherein the spring force for clamping the workpiece can readily be adjusted to accommodate variations in thickness of the sheet to be bent.
In accordance with the invention, the generally oval shaped spring device is made of two members, each of which has front and rear walls with the front walls pivoted to one another to vary the force between the front and rear walls and the pivotal relationship of the two members thereby accommodating the sheet bending brake to workpiece of differing and varying thicknesses.